Potential for ground charcoal for synthetic dye removal

Abstract

The potential for ground charcoal for synthetic dye removal was investigated in a series of batch experiments. Ground charcoal from black wattle tree was used to remove a synthetic dye, Congo red from water through sorption. Equilibrium time, rate studies, effect of pH on the dye removal, percentage removals and sorption isotherms were investigated. The Equilibrium time for the particle size studied was found to be 18 hours. The long Equilibrium time obtained indicated that adsorption was a <slow process. Possible causes of slow attainment to equilibrium could be due to slow molecular diffusion into the adsorbing sites in the micropores, formation of new bonds between the dye molecules and the charcoal, and slow reaction at the surface between the dye and the charcoal. The percentage dye removals decreased with increase in concentration. The removal was predominant in the low concentrations, below 20mg/l. The pH in the range of 4-9 had no any effect on the removal of the dye. Increase in pH beyond pH 9, however, resulted in decreased dye removal. The data analyzed was found to correspond to Freundlich's isotherm model with correlation coefficients ranging between 0.9014and 0.9798. This indicated that the isotherm represented the data well. The constants in the model, k and n ranged between 0.8481-1.915 and 0.5357-0.4298, respectively The mechanism through which the dye was adsorbed could be through coverage of the active sites in the charcoal and once covered, the adsorption capacity of the charcoal diminished. A similar trend for the effect of mass of ground charcoal on the removal of the dye was observed indicated that the mechanism of removal predominant is most effective for low dye concentrations, below 20mg/l.